Pressure vessels are conventionally composed of structural sections having flanges or other connectors at their extreme ends. The flanges are secured to the assembly by securing bolts that extend through the mating flanges. The opposed flanges may be drawn together about a metal sealing ring with sufficient force to cause metal-to-metal sealing between surfaces on the seal ring and tapered surfaces on the opposing seal grooves in the first and second members.
An API seal ring may leak under circumstances where the bolts are properly tightened to secure the flanges in sealed engagement, but thereafter excessive heat causes bolt extension such that the flanges are allowed to be moved apart a slight amount. When this occurs, there may be insufficient mechanical force between the seal ring and the mating wall surfaces of the seal groove to maintain a fluid tight seal. Also, when the flange bolts are made up very tightly, metal coining between the seal ring and the mating wall surfaces may occur, in which case only a slight movement of the flanges may cause seal leakage. Coining of the seal ring typically occurs, because the seal ring metal is less hard than the metal defining the receiving grooves in the flange. Overstressing the studs to shut off a leak may also cause coining of the seal ring groove. It is frequently recommended to employ periodic tightening of flange bolts to prevent leaking in high temperature applications.
U.S. Pat. No. 4,410,186 discloses a seal ring for flanged joints, and was part of a seal concept for nuclear reactor applications. Due to wide tolerances, an API seal ring groove would be coined by this type of seal ring. To eliminate coining, one would have to make several sizes of a seal ring for a specific ring groove. This type of seal ring also would not seem suitable for holding pressures at high temperatures when the studs elongate because of its limited flexibility.
U.S. Pat. No. 5,058,906 discloses a seal ring formed from a high strength material. For the seal ring to function, the ring flexes against the ring groove wall to burnish and form a seal. The seal ring is intended to flex within its elastic limits, and again would require numerous different seal rings to work satisfactorily within a single API ring groove.
U.S. Pat. No. 5,240,263 discloses a seal ring with a substantial uniform cross sectional thickness. The patent teaches substantially planar contact between surfaces of the seal ring and the tapered surfaces defining the seal groove. This type of seal may leak because there is no pressure energization. Because the seal areas are large, pressure can migrate into the seal area thus equalizing pressure, resulting in leakage.
The disadvantages of the prior art are overcome by the present invention, and an improved seal ring and method are hereinafter disclosed for reliable sealing between two members.